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Full text of "Handbook Of Chemical Engineering - I"

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plish more effective breaking. Dodge type machines are not widely used, due to their comparatively small capacity and consequently, increased installation cost per ton of product.
Gyratory.The second type of rock machine ordinarily used is the Gyratory. Essentially this type of breaker consists of a central pillar shaft fixed at its uppermost point and provided with means of gyration at its lowest point. On this shaft is fixed a renewable crushing head in the shape of a frustum of an upright cone. This head gyrates inside of an inverted conical concave, the inner surface being lined with renewable wearing plates. The receiving opening of machines of this type is, therefore, annular and breaking is accomplished by the alternate advance and recession of the crushing head with respect to the concaves. Since the movement is gyratory, it is continuous, so that while the head is approaching one point of the concave, it is receding from the point diametrically opposite. There are no reciprocating elements and the power is applied continuously to crushing work. Since the point of greatest gyration is usually some distance below the point of breaking, the advantage of leverage is embodied. In this machine, the breaking is effected by a combination of compression, roll action and beam action. As the crushing surfaces approach each other, compression is brought into play and since the crushing head is always traveling, the friction between the rock and the head causes it to revolve, thereby bringing into play roll action since the head rolls over the rock being broken.
Since in an annular opening of this kind, a tabular piece of rock would necessarily be fixed at its ends and unsupported at its middle point, beam action is brought into play and the rock will be broken at about its middle point. Since the radius of gyration is not great in any case, the discharge opening does not vary greatly and the angle of nip is not subject to great variation. As a result, the product of machines of this type is much more uniform than with other types, and more cubical in character.
The  gyratory breaker is practically a stage-breaking machine, since a piece of rock approximating  the   maximum   capacity of the angular opening will be reduced in successive stages by means of successive nips of the large piece and of the resulting smaller pieces into
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